U.S. patent number 4,048,375 [Application Number 05/708,603] was granted by the patent office on 1977-09-13 for magnetic recording media of improved mechanical resistance.
This patent grant is currently assigned to BASF Aktiengesellschaft. Invention is credited to Hans-Joerg Hartmann, Helmut Jakusch, Gustav Loewenberg, Herbert Motz, Dieter Schaefer.
United States Patent |
4,048,375 |
Loewenberg , et al. |
September 13, 1977 |
Magnetic recording media of improved mechanical resistance
Abstract
Magnetic recording media consisting of a non-magnetic base and,
applied thereto, a firmly adhering magnetic coating based on finely
divided magnetic pigment dispersed in organic binders, which
coating contains, according to the invention, salts of long-chain
basic polyaminoamides with high molecular weight organic acid
esters. Such magnetic recording media exhibit improved mechanical
resistance and improved adhesion of the coating to the base,
coupled with advantageous electromagnetic properties.
Inventors: |
Loewenberg; Gustav
(Ludwigshafen, DT), Hartmann; Hans-Joerg (Freinsheim,
DT), Schaefer; Dieter (Lindenberg, DT),
Motz; Herbert (Ludwigshafen, DT), Jakusch; Helmut
(Ludwigshafen, DT) |
Assignee: |
BASF Aktiengesellschaft
(Ludwigshafen, DT)
|
Family
ID: |
5953563 |
Appl.
No.: |
05/708,603 |
Filed: |
July 26, 1976 |
Foreign Application Priority Data
Current U.S.
Class: |
428/475.2;
252/62.54; 428/477.7; 428/900; 428/843.7; G9B/5.251; G9B/5.243 |
Current CPC
Class: |
G11B
5/70 (20130101); G11B 5/7028 (20130101); Y10S
428/90 (20130101); Y10T 428/31765 (20150401); Y10T
428/31736 (20150401) |
Current International
Class: |
G11B
5/702 (20060101); G11B 5/70 (20060101); H01F
010/02 () |
Field of
Search: |
;427/127-132,48
;252/62.54 ;428/423,457,458,474 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Pianalto; Bernard D.
Attorney, Agent or Firm: Keil, Thompson & Shurtleff
Claims
We claim:
1. In a magnetic recording medium comprising a non-magnetizable
base and, applied thereto, a firm adhering coating suitable for
magnetic recording and consisting essentially of a finely divided
magnetic powder dispersed in an organic polymeric binder, the
improvement which comprises: including in said coating from 0.2 to
5% by weight, based on the total weight of the coating, of a
neutral salt of (a) a basic polyaminoamide, obtained by condensing
dimerized and trimerized unsaturated fatty acids with aliphatic
polyamines possessing two primary amino groups and having an amine
value of from 100 to 500 and (b) an organic acid ester, obtained by
reacting equimolar amounts of a polyalkylene glycol of molecular
weight from 100 to 500, a monocarboxylic acid of 10 to 22 carbon
atoms and a dicarboxylic acid anhydride or a dicarboxylic acid of 2
to 8 carbon atoms.
2. A magnetic recording medium as set forth in claim 1 wherein the
amount of said neutral salt is from 0.5 to 3% by weight based on
the total weight of the coating.
3. A magnetic recording medium as set forth in claim 1, wherein the
organic acid ester (b) is obtained by reacting equimolar amounts of
a polyalkylene glycol selected from the group consisting of
polyethylene glycol and polypropylene glycol having a molecular
weight of from 150 to 500, a fatty acid of 10 to 18 carbon atoms
and a dicarboxylic acid of 2 to 8 carbon atoms.
4. A magnetic recording medium as set forth in claim 1 wherein said
aliphatic polyamine is selected from the group consisting of
diethylenetriamine, triethylenetetramine, tetramethylenepentamine,
1,4-diaminobutane, 1,3-diaminobutane, hexanemethylenediamine,
diacetoneamine, 3-(N-isopropylamino)-propylamine and
3,3'-imino-bis-propylamine.
Description
The present invention relates to magnetic recording media
consisting of a non-magnetic base and, applied thereto, a firmly
adhering magnetic coating based on finely divided magnetic pigment
dispersed in organic binders, which magnetic coating contains salts
of long-chain polyaminoamides and high molecular weight acid esters
in addition to other dispersing agents and additives for improving
the mechanical resistance of the coating.
Magnetic recording media are used to record audio and video signals
and digital data, and depending on the type of recording the
mechanical properties, in particular, of the magnetic coating have
to meet different requirements.
In the case of video and computer tapes the speed between the tape
and the magnetic head is very high. To withstand this stress, the
adhesion of the coating to the base, and the resistance of the
coating to abrasion by parts of the apparatus in the tape path are
of particular importance. Computer tapes are subjected to severe
stresses particularly in the case of frequent reversals, the
stresses being caused not only by the capstan and pinch roll but
also by the sliding contact between the tape and head. Depending on
the type of drive unit and the degree of wear of the magnetic head,
it can happen, with frequently used tapes, that damage to the
magnetic coating results in an increasing number of write and read
errors and even in the irreversible loss of data.
Magnetic discs, used in modern data processing units, are operated
at speeds of up to 3,600 rpm. The magnetic heads, due to their
aerodynamic shape, fly at a small distance above the surface of the
disc on a cushion of air which is produced by rotation of the disc.
The distance between the disc surface and the magnetic head can be
as little as 0.5.mu.u. With such small distances, microscopic
foreign particles, such as dust, or the slightest unevenness in the
coating, can suffice to disturb the flight of the magnetic head to
a degree which causes contact between the head and the disc. This
can result in the loss of data or in damage to the magnetic disc.
The deposits of coating material on the head and on the surface of
the disc can easily lead to head crashes because they interfere
with the flight of the magnetic head, and such crashes can result
in the destruction of the magnetic head and render the disc pack
unusable. Hence, the data-bearing layer of magnetic discs, which in
general is from 1.0 to 2.0.mu.u thick because of the high
resolution required, also has to meet high standards as regards
mechanical resistance.
The reliability of audio tapes, e.g. tapes for amateur use and
cassette tapes, depends greatly on the abrasion resistance of the
magnetic coating even under extremely unfavorable climatic
conditions, e.g. high temperature and high atmospheric humidity,
and also under unfavorable apparatus conditions, e.g. as found with
apparatus where the parts which come into contact with the tape are
badly worn and can therefore have a very abrasive effect on the
tape surface. The occurrence of one or more of these factors, in
conjunction with inadequate abrasion resistance of the coating, can
result in deposits of coating material on the magnetic head and on
the parts of the apparatus in the tape path, such as the capstan
and guide pins, and this in turn can result in a poor recording and
playback signal level, and/or in wow and flutter. Tapes with
inadequate abrasion resistance, used under unfavorable conditions,
necessitate constant cleaning of the soiled parts of the
apparatus.
The addition of solid or liquid lubricants, such as graphite,
molybdenum disulfide, stearic acid, oleic acid, fatty acid esters,
fatty acid amides, squalenes and paraffin waxes, to the magnetic
coating, in order to provide abrasion-resistant magnetic recording
media, has been disclosed. As stated in German published
application No. 1,278,513, many of the known lubricants, e.g. fatty
acid esters, tend to exude easily and cause undesirable tackiness
of the coating. The addition of fatty acid esters such as stearyl
stearate also gives unsatisfactory electo-acoustic and video
recording properties. Furthermore, these additives, as well as the
addition of fatty acids such as n-stearic acid or mixtures of fatty
acid amides and paraffin wax, tend to produce deposits on the parts
with which the tape comes into contact. In addition, most
lubricants have a plasticizing action on the binder contained in
the magnetic coating.
It is an object of the present invention to provide magnetic
recording media which exhibit better mechanical resistance and
anchorage of the coating than prior art products, while having
advantageous electromagnetic properties.
We have found that this object is achieved and that magnetic
recording media comprising a non-magnetizable base and, applied
thereto, a firmly adhering coating suitable for magnetic recording
and consisting essentially of a finely divided magnetic powder
dispersed in an organic polymeric binder, exhibit particularly
advantageous properties and improved mechanical resistance if the
said coating contains from 0.2 to 5 per cent by weight, based on
the total weight of the coating, of a salt of
a. a basic polyaminoamide, obtained by condensing dimerized and
trimerized unsaturated fatty acids with aliphatic polyamines
possessing two primary amino groups and
b. an organic acid ester, obtained by reacting equimolar amounts of
a polyalkylene glycol of molecular weight from 100 to 500, a
monocarboxylic acid of 10 to 22 carbon atoms and a dicarboxylic
acid anhydride or a dicarboxylic acid of 2 to 8 carbon atoms.
The organic salts contained in the magnetic coating of the magnetic
recording medium of the invention are obtained by reacting a basic
polyaminoamide with a polymeric ester which contains carboxyl
groups. The basic component of the salt, i.e. the polyaminoamide,
is preferably manufactured by conventional methods, by reacting
fatty acid oligomers with polyamines such as diethylenetriamine,
triethylenetetramine, tetramethylenepentamine, 1,4-diaminobutane,
1,3-diaminobutane, hexanemethylenediamine, diacetoneamine,
3-(N-isopropylamino)-propylamine, 3,3'-amino-bis-propylamine and
similar amines (cf. Houben-Weyl, Methoden der organischen Chemie,
4th Edition, Volume XIV/2, Stuttgart 1963, pages 523-525). Of the
fatty acid oligomers which are employed for the manufacture of the
polyaminoamides, those produced by dimerizing or trimerizing
unsaturated fatty acids or drying oils, their free acids, such as
linoleic acid, or the esters of these acids with monohydric
alcohols, are particularly suitable. Suitable commercially
available products are the .RTM.VERSAMID resins from General Mills,
Inc. A method of maufacture of the acid component of the salt is to
react a polyalkylene glycol having a molecular weight of from 100
to 500 with an equimolar amount of a saturated or unsaturated,
straight-chain or branched fatty acid of 10 to 22 carbon atoms so
as to esterify one of the two OH groups, and to react the resulting
product with a dicarboxylic acid anhydride or a dicarboxylic acid
of 2 to 8 carbon atoms. It is particularly advantageous to react a
polyethylene glycol or a polypropylene glycol (e.g. of molecular
weight 150 to 500), and especially the corresponding trimeric
alkylene glycols, with a monocarboxylic acid of 10 to 18 carbon
atoms, e.g. oleic acid or ricinoleic acid, and a dicarboxylic acid
of 2 to 8 (e.g. 4 to 6) carbon atoms, e.g. maleic acid or adipic
acid, to give the diester which possesses a free acid group.
The resulting carboxylic acid and the polyaminoamide are then
reacted with one another, advantageously in such weight ratios that
a neutral salt is produced. The reaction can, if appropriate, be
carried out in a suitable polar or non-polar solvent.
When producing the magnetic coating, the above salts are added in
an amount of from 0.2 to 5 percent by weight, preferably from 0.5
to 3 percent by weight, based on the dry weight of the magnetic
coating. A ratio of from 3 to 5 parts by weight of magnetic
pigment, especially gamma-iron (III) oxide of chromium dioxide, to
about 1 part by weight of binder, from 0.05 to 0.5 part by weight
of other additives, e.g. dispersing agents and, e.g., additives for
improving the electrical conductivity of the magnetic coating, and
from 0.05 to 0.2 part by weight of the organic salts added
according to the invention, has proved very advantageous.
Preferred magnetic pigments are finely divided acicular
gamma-iron(III) oxide having a length of from 0.1 to 2.mu.u and
especially from 0.1 to 0.9.mu.u or acicular chromium dioxide of the
same length. Further suitable magnetic pigments are cubic
gamma-iron(III) (III) oxide modified with heavy metals, especially
cobalt, and finely divided metal alloys of iron, cobalt and/or
nickel.
Further additives for the production of magnetic coatings, such as
dispersing agents, e.g. lecithins, small amounts of a
monocarboxylic acid or of mixtures of monocarboxylic acids, in the
case of chromium dioxide preferably zinc oleate, zinc stearate or
zinc isostearate, and fillers, e.g. conductive carbon, graphite,
quartz powder and/or non-magnetizable silicate-based powders, and
flow improvers, e.g. small amounts of silicon oil, can be added to
the magnetic dispersions. The total amount of these additives
should advantageously not exceed 12 percent by weight, and
preferably not exceed 8 percent by weight, based on the dry weight
of the magnetic coating.
Suitable binders for the preparation of the magnetic dispersion are
those conventionally used for the production of magnetic coatings,
e.g. alcoholic solvent-soluble copolyamides, polyvinylformals,
polyurethane elastomers, mixtures of polyisocyanates and
polyhydroxylic compounds, vinyl chloride polymers containing more
than 60% by weight of polymerized vinyl chloride units, e.g. vinyl
chloride copolymers with comonomers such as vinyl esters of
monocarboxylic acids of 2 to 9 carbon atoms, esters of aliphatic
alcohols of 1 to 9 carbon atoms and ethylenically unsaturated
carboxylic acids of 3 to 5 carbon atoms, e.g. the esters of acrylic
acid, methacrylic acid or maleic acid, or these carboxylic acids
themselves, and vinyl chloride copolymers which contain hydroxyl
groups and can be manufactured by partial hydrolysis of vinyl
chloride/vinyl ester copolymers or by direct copolymerizaton of
vinyl chloride with monomers containing hydroxyl groups, e.g. allyl
alcohol, 4-hydroxybutyl methacrylate or acrylate, or
2-hydroxylethyl methacrylate or acrylate, or 2-hydroxyethyl
methacrylate or acrylate. Further suitable binders are mixtures of
polyurethane elastomers with polyvinylformals, phenoxy resins and
vinyl chloride copolymers of the stated composition. Preferred
binders are polyvinylformal binders and polyurethane elastomer
mixtures of the stated type, above all mixtures with
polyvinylformals. Preferred polyurethane elastomer binders are
commercially available elastomeric polyester-urethanes obtained
from adipic acid, 1,4-butanediol and
4,4'-diisocyanatodiphenylmethane.
When using flexible bases, particularly suitable binder mixtures
for the production of the magnetic recording media of the invention
are mixtures consisting of from 20 to 90 percent by weight of an
elastomeric polyurethane which is virtually free from isocyanate
groups, is soluble in a volatile organic solvent and has been
obtained from a linear aliphatic polyester or polyether and a
diisocyanate of 6 to 24 carbon atoms; and from 10 to 80 percent by
weight of a vinyl chloride copolymer which contains from 50 to 90
percent by weight of vinyl chloride units, and from 10 to 50
percent by weight of units of at least one diester of maleic acid
with an alcohol of 1 to 3 carbon atoms, or from 10 to 80 percent by
weight of a phenoxy resin produced from bisphenol A and
epichlorohydrin.
Magnetic dispersions which are particularly suitable for the
production of rigid magnetic discs preferably contain binders such
as epoxy resins, phenoxy resins, aminoplast precondensates,
polyester resins, polyurethanes or polyurethane-forming reactants
and mixtures of such binders with one another or with other
binders, such as polycarbonates or vinyl polymers, e.g. vinyl
chloride copolymers or vinylidene chloride copolymers or
heat-curable acrylate or methacrylate copolymers.
The preferred binder for the manufacture of the magnetic discs is a
mixture of from 60 to 70% by weight of a solid curable
polycondensate of 2,2-bis-(4-hydroxyphenyl)-propane and
epichlorohydrin having an epoxy equivalent weight of from about 400
to 2,500 and a melting point of from about 50.degree. to
150.degree. C, from 10 to 30% by weight of a curable
allyloxybenzene-formaldehyde condensate of the resol type with free
methylol groups or with methylol groups etherified with a lower
alcohol, the condensate having a molecular weight of less than
1,000 and from 10 to 30% by weight of a curable
melamineformaldehyde condensate with more than two methylol groups
etherified with n-butanol or iso-butanol, the condensate having a
molecular weight of less than 2,500.
Suitable organic solvents for the preparation of the magnetic
dispersion are those conventionally used for this purpose,
especially aromatic hydrocarbons, e.g. benzene, toluene or xylene,
alcohols, e.g. propanol or butanol, ketones, e.g. acetone or methyl
ethyl ketone, ethers, e.g. tetrahydrofuran or dioxane, and mixtures
of such solvents, and other solvents and solvent mixtures
conventionally used for surface-coating binders.
It has proved advantageous to employ the above-mentioned organic
salts of the polyaminoamides from the start of the dispersion
operation, in the conventional apparatus used for this purpose,
together with the magnetic pigment, the additives, a part of the
binder and an amount of organic solvent sufficient to bring the
viscosity of the mixture to an advantageous value. However, it is
also possible to admix the organic salts, added according to the
invention, during subsequent processing, up to the point directly
before the finished dispersion is applied to the base.
The magnetic recording media of the invention can be manufactured
by conventional methods. Advantageously, the dispersion produced in
dispersing equipment, e.g. a tube mill or a stirred ball mill, from
the magnetic pigment and a solution of the binder or binders, in
the presence of dispersing agents and other additives, is filtered
and is applied to the non-magnetic base by means of conventional
coating equipment, e.g. by means of a knife coater. As a rule,
orientation of the magnetic particles is carried out before the
fluid coating mixture is dried on the base; drying is
advantageously carried out for from 2 to 5 minutes at from
50.degree. to 90.degree. C.
Suitable non-magnetic bases for the magnetic coating are those
conventionally used for this purpose, e.g. films of the usual
thickness based on polyvinyl chloride or polyesters such as
polyethylene terephthalate films. The application of an
adhesion-promoting intermediate coating, e.g. one based on a
vinylidene chloride copolymer, to the base, before applying the
magnetic coating, is feasible and sometimes advantageous.
The magnetic coating can be calendered on conventional equipment by
passing them between polished rollers optionally heated to
temperatures of from 50.degree. to 100.degree. C, preferably from
60.degree. to 80.degree. C. The thickness of the magnetic coating
is in general from 3 to 20.mu.u and preferably from 8 to 15.mu.u.
For the production of magnetic tapes, the coated webs of base
material are slit lengthwise to the conventional widths.
When producing magnetic coatings for magnetic discs, it has proved
advantageous to apply the dispersion, containing the magnetic
pigment, radially to the slowly rotating substrate and then to
distribute the dispersion over the substrate by rotating it at high
speed. For this purpose, conventional non-magnetic metallic
substrates of the usual sizes and thicknesses, made from aluminum
or aluminum alloys, can be used. For the manufacture discs with
thin magnetic coatings it is advantageous to use substrates having
polished surfaces.
Compared to conventional magnetic recording media of the same type,
the magnetic recording media of the invention are distinguished by
improved mechanical resistance and improved anchorage of the
coating, coupled with very advantageous electromagnetic
properties.
The following Examples and Comparative Experiments illustrate the
advantages of the magnetic recording layer of the invention when
used on computer tape, audio cassette tape and magnetic discs.
Parts and percentages in the Examples are by weight, unless stated
otherwise.
EXAMPLE 1
A. Preparation of the polyaminoamide salt I
1 mole of triethylene glycol, 1 mole or ricinoleic acid and 1 mole
of adipic acid are esterified. 1 part of the resulting diester is
dissolved in 2 parts of tetrahydrofuran and a solution of 0.5 part
of a polyaminoamide having an amine number of about 210-230 and a
viscosity of 40.degree. C of 500-750 poise, and containing 6.48
milliequivalents of amine hydrogen/g, e.g. .RTM.VERSAMID 115 of
General Mills Co., in 1 part of tetrahydrofuran, is added in the
course of about 30 minutes. The mixture is heated at 50.degree. C
for about 2 hours and the solvent is then distilled off.
B. Preparation of the polyaminoamide salt II
1 mole of polypropylene glycol having a molecular weight of about
500, 1 mole of oleic acid and 1 mole of maleic anhydride are
esterified. 1 part of the resulting diester is dissolved in 2 parts
of tetrahydrofuran and a solution of 0.16 part of a polyaminoamide
having an amine number of 325-360 and a viscosity of 40.degree. C
of 44 poise, and containing 9.99 milli-equivalents of amine
hydrogen/g, e.g. .RTM.VERSAMID 140 of General Mills Co., dissolved
in 0.32 part of tetrahydrofuran, is added in the course of about 30
minutes. The mixture is heated at 50.degree. C for about 2 hours
and the solvent is then distilled off.
EXAMPLE 2
Computer tape
EXAMPLES 2A, 2B AND COMPARATIVE EXPERIMENT (EXAMPLE 2C)
The magnetic coatings shown below (Table 1) were produced by prior
art processes. The base used was a 36.mu.u thick polyethylene
terephthalate film.
TABLE 1 ______________________________________ Example Example
Comparative 2A 2B Example 2C Composition (%) (%) (%)
______________________________________ gamma-iron(III) oxide 71.4
72.2 73.0 conductive carbon 4.2 4.3 4.4 phenoxy resin .sup.30 (1)
4.2 4.2 4.2 polyurethane .sup.+ (2) 16.3 16.5 16.7 di-n-octyl
sebacate 0.8 -- 0.7 soybean lecithin 1.0 1.0 1.0
dimethylpolysiloxane .sup.+ (3) -- 0.7 -- polyaminoamide salt I 2.1
-- -- polyaminoamide salt II -- 1.1 --
______________________________________ .sup.+ (1) phenoxy resin
manufactured from bisphenol A and epichlorohydrin, molecular weight
30,000. .sup.+ (2) elastomeric isocyanate-free linear polyurethane
manufactured from adipic acid, 1,4-butanediol and .sup.+ (3)
viscosity: 150 cp.
Computer tape test
15 cm lengths of tape from Example 2A, Example 2B and Comparative
Example 2C were each subjected to 50,000 passes on an IBM 2401
computer tape drive. The increase in drop-outs, the waveform of the
playback signal, the condition of the tape surface and the amount
of material abraded from the tape and deposited on the magnetic
head was assessed. The degree of abrasion is assessed visually by
stripping the deposit from the pole faces of the head by means of
adhesive tape and sticking the latter onto white paper, and is
classified according to a 6-rating scale, 1 denoting no abrasion
and 6 very marked abrasion. To determine the anchorage, no incision
is made across the coating with a knife. An adhesive tape is stuck
over the damaged area and then pulled off with a sharp tug. The
extent to which the coating continues to tear from the incision is
assessed.
__________________________________________________________________________
Results Example 2A Example 2B Comparative Example 2C
__________________________________________________________________________
increase in errors 0 0 0 tape surface unchanged unchanged polished
shallow grooves in the longitudinal direction waveform of the drops
in original drops in original drops in original signal on outer
signal level of signal level of signal level of 40% tracks 10% 15%
deposits of coating material on the magnetic head rating 1 1 3
anchorage no tearing no tearing coating tears for about 1 cm from
the incision
__________________________________________________________________________
EXAMPLE 3
Audio cassette tape
EXAMPLES 3A and 3B AND COMPARATIVE EXPERIMENT (EXAMPLE 3C)
The magnetic coatings shown below (Table 2) were produced by prior
art processes. The base used was a 12.mu.u thick polyethylene
terephthalate film.
TABLE 2 ______________________________________ Example Example
Comparative 3A 3B Example 3C Composition (%) (%) (%)
______________________________________ gamma-iron(III) oxide 78.8
79.2 79.7 vinyl chloride 5.4 8.9 8.9 copolymer .sup.+ (1)
polyurethane .sup.+ (2) 12.3 8.9 8.9 silicone oil .sup.+ (3) 0.5
0.6 0.5 lecithin -- 0.8 2.0 polyaminoamide salt I 3.0 -- --
polyaminoamide salt II -- 1.6 --
______________________________________ .sup.+ (1) Vinyl
chloride/dialkyl maleate copolymer containing 80% of vinyl chloride
units, 10% of dimethyl maleate units and 10% of diethyl maleate
units. .sup.+ (2) Elastomeric isocyanate-free linear polyurethane
manufactured from adipic acid, 1,4-butanediol and
4,4-diisocyanatodiphenylmethane. .sup.+ (3) dimethylpolysiloxane
having a viscosity of 150 cp.
Audio cassette tape test
A signal having a frequency of 10 kc/s is recorded on a cassette
tape over a length of about 200 cm. The length of tape is then
rewound in contact with the magnetic head and the recorded signal
is reproduced, the playback voltage being recorded on a graphic
recorder. After this, the length of tape is rewound again, the old
recording is erased and a 10 kc/s signal is again recorded and
reproduced. This procedure is repeated a total of 50 times. Since a
new recording is made each time, this test is also very suitable
for detecting slight deposits on the head and coating wear. The
experiment is carried out at room temperature and 40.degree. C. The
drop in signal level and the amount of abraded material deposited
on the pole faces of the recording and reproducing head can be
taken as a measure of the wear resistance of the tape. The degree
of abrasion is assessed as described in Example 2.
______________________________________ Example Example Comparative
Results 3A 3B Example 3C ______________________________________ a)
room temperature: drop in signal level (db) 0 0.5 4 deposits on
head, rating 1 1 2-3 b) 40.degree. C: drop in signal level (db) 0
1.5 6 deposits on head, rating 1 1-2 2-4
______________________________________
EXAMPLE 4
Magnetic discs
EXAMPLES 4A AND COMPARATIVE EXPERIMENT (EXAMPLE 4C)
The magnetic coatings for magnetic memory discs shown below (Table
3) were produced by prior art processes. The substrates used were
aluminum discs, onto which the coating was baked at about
260.degree. C.
TABLE 3 ______________________________________ Composition of
magnetic Example Example Comparative coating 4A 4B Example 4C
______________________________________ iron(III) oxide 48.0 48.0
48.5 fused alumina 2.4 2.4 2.4 dimethylpolysiloxane .sup.+ (1) 0.5
0.5 0.6 epoxy resin .sup.+ (2) 28.9 28.9 29.1 melamine-formaldehyde
9.6 9.6 9.7 resin .sup.+ (3) phenol-formaldehyde 9.6 9.6 9.7 resin
.sup.+ (4) polyamindamide salt I 1.0 -- -- polyaminoamide salt II
-- 1.0 -- ______________________________________ .sup.+ (1)
Viscosity of a 70% strength solution in xylene: 700 - 1,000 cp
.sup.+ (2) Epoxy resin manufactured from bisphenol A and
epichlorohydrin, epoxy equivalent weight about 1,850. .sup.+ (3)
Melamine-formaldehyde resin etherified with butanol, molecular
weight about 2,000. .sup.+ (4) Allyloxybenzene/formaldehyde
condensate of the resol type, molecular weight about 310.
Disc test
To test the adhesion of the magnetic coating to the aluminum
surface, roughened, square pieces of aluminum havng a surface area
of 1 cm.sup.2 are glued onto the surface of the magnetic coating by
means of an epoxy/polyamine 2-component adhesive, which is then
cured for 1 hour at 80.degree. C. The force required to tear off
the aluminum cube is then measured. To test the resistance to
mechanical wear, the magnetic disc is rotated at a speed of 2,400
rpm on a test drive unit. A ceramic body having the shape of a
magnetic write-and-read head is then caused to fall synchronously
onto the magnetic disc from a distance of 5 mm, with a force of 300
g. In this test, the head lands in a zone which covers only 1/20 of
the total track length (about 1 m). The wear resistance of the
magnetic coating is assessed in terms of the number of crashes
required to wear down the magnetic coating to the aluminum
substrate.
______________________________________ Example Example Comparative
Test results 4A 4B Example 4C
______________________________________ adhesion (N/cm.sup.2) 950
1,100 600 wear test (number of crashes) >1,500 1,300 1,000
______________________________________
* * * * *